Check out my thread titled Monster cluster repair If you’re clocks are different then disregard the following. I’ve seen several threads related to faulty rectifier/regulator but in my case it was purely down to the stepper motor which drives the needle. The crank position sensor CPS feeds signals to the ECU which subsequently drives the clock. The main thing is the CPS signal to ECU as the tach is purely visual info and does not affect engine. If you have access to a signal generator you can drive the clocks with a square wave to replicate the signal from the ECU. A damaged final gear gives these symptoms as it slips as the motor revolution tries to reflect engine speed but loses sync with effectively the needle. The final gear is available separately for about £6 but you need to strip clocks which I found fairly easy once I got the knack of removing the needles. Hope this helps
Update...I wiggled the connecter and got the tach to briefly work , but not consistently and for like 2 seconds it worked normal....so I pulled the tach apart...everything looks fine...all connectors on the board are fine...I tightened the 3 screws you see on the back that hold the “motor” to the chipboard s..put it back on the bike and got no results besides it now goes up to 5k instead of 4 and stops.....I wiggle the white connecter and it won’t even make the tach go crazy like it did when I wiggled it before I took it apart....I’m just buying a new tach and hope that one works , if it doesn’t then I’ll return it and have to go from there...does anyone know any more ways I can rule out anything else so that I know for sure it’s the tach unit? I wanna know what the voltage should be coming from the eco to the tac so I can make sure it’s correct?!?
Do you mean clock as in the clock speed signal used by the computer? I don’t wanna sound dumb, but I wasent sure ....I don’t have the M Marelli cluster...I’m pretty good with electronics and have the tools,I’m just a bit rusty. I was real into building by own circuit boards when I was a kid , it’s been a while and I have a background in hardware working on computers...so if you or anyone could help me I’d really like to figure this out....this is my what it looks like inside....there’s some corrosion on what looks to be a “variable switch” I guess.I could call it..otherwise everything looks fine just going by looks .I’m assuming for making fine adjustments ...like I said I’m no electronics pro, gotta do some studying.... Or i spend 80$ for a used instrument cluster(a lot less work)...but my last resort
Should help to check motor out. Here’s the chip and some data. https://www.ebay.com/itm/CS-CS289-DIP-14-20mA-Air-Core-Tachometer-Drive-Circuit-/273703080448 Data sheet https://pdf1.alldatasheet.com/datas...RRY/CS289/+_587JUv.DRS/1cGVNEG+/datasheet.pdf New designs have now moved on but if your interested on how they use the cs289 with this type of technology check out the newer device. https://www.onsemi.com/pub/Collateral/CS8190-D.PDF
Here’s a useful response on Ducati.ms if it helps. As the guy says it’s a fairly simple circuit with very few components and assuming the meter is okay a relatively cheap fix if you discount time spent on fixing. Here’s the link but if doesn’t work I copied and pasted. https://www.ducati.ms/forums/40-sport-touring/140971-st4s-rev-counter-tachometer-repair.html People have said that they can be opened and fixed but I couldn’t find any pictures etc after a search so thought I would rectify that situation. It was fiddly but well worth the time spent as (for now at least) it works well. Symptoms were that the needle was sticking at 7k and not responding at tickover. The first tear down to check it over followed by tightening up the brass screws at the back made it worse as tickover was then showing as 4000 rpm so it was at that point that I thought I had better work out how it works…. First check is that the feed to the tach via the 3-pin connector is working properly. There are two bullet connector feeds for the immobiliser led but this is completely separate to the rev-counter function and only shares the common housing. The grey and black wire on the main connector for the tach is the earth whilst the light blue wire is +12V. These are obviously easy to check. The green wire feed is from the ECU and feeds a square wave signal to the tach electronics and so is harder to check. I managed to borrow an ancient oscilloscope to check the signal and it was a nice clean square wave with a frequency of about a third of the engine rpm (ie about 333 hz at tickover). As expected, the frequency increases proportionally as the engine is revved. Measuring the voltage at the centre pin with a multimeter set to DC gave me about 1 volt less than battery voltage with the ignition on and about 2.5V with the engine running (not changing with rpm) so that may help diagnose for those without oscilloscope. Now confident the wiring was working, I set to with the Dremel and a cut-off disk and split the housing about 1” below the bezel. There is nothing to damage at that level. Removing the 3 brass sleeve nuts at the back then allow the circuit board to be separated from the needle movement. It’s a fairly basic circuit and a bit of research into the IC (CS289) reveals that it is an industry standard air-core tachometer drive circuit. A simple internet search revealed a data-sheet which allowed me to understand the basics. The circuit takes the signal from the incoming square wave and converts it to three DC feeds (corresponding to the 3 connections mediated via the brass sleeve nuts to the meter movement). There is a reference voltage feed Vz along with Vsine and Vcosine feeds. Basically, the meter movement has two sets of windings at 90 degrees apart connected together at the Vz feed. Varying the magnitude of the Vsine and Vcosine voltages forces the needle to a certain degree of rotation. Each meter winding should be about 200 ohms. In my case, a quick check showed only one working winding. Thus, I popped off the needle and unscrewed the dial to allow me to remove the meter movement. It then became clear that when I had tightened one of the brass screws, the whole mounting post had twisted and broke the very fine wire feed from the coil (hopefully clear from the picture). I managed to re-solder the connection and then used Plastech to reinforce the post to (hopefully) prevent it twisting on reassembly. I then reassembled and checked that all is well at the brass connections at the rear (200 ohms across two of the connectors and 400 ohms across the other). The difficulty is now putting the needle back in the right place! My first guess resulted in a working tacho but it was showing a tickover at 2,500 rpm. I suspect they apply a calibrating signal when they build them and then pop the needle on at the appropriate place. I resorted to letting the bike tickover at what was previously a reliable 1000 rpm and then popped the needle back so it read what it did before. Its probably not as accurate as the factory method but will be close enough for normal riding. Now happy it was working again, I used Plastech to ‘glue’ the housing back together again and finished it off with Duck tape. Once mounted back in the dash the repair is invisible. Not sure how long it will last but it kept me quiet for a few hours The main message should be that be careful not to tighten up those brass screws too tight or you risk breaking a connection in the meter in the same way I did. They should only be nipped up. If tightening them doesn’t work then get a multimeter and check you have 200 ohms across two of the brass connectors and 400 ohms across the other. If that is OK then you have no need to dismantle the meter movement so check the circuit board for dry joints or fracture. It’s a pretty basic circuit so any electronics repair guru should be able to trouble shoot and fix it.
Omg this is just what I needed !! Thanks for finding that. I ordered a used instrument cluster on eBay. But I will return it if I can still fix this one. I'll check back. Gonna read this in depth and work on it !! Your awesome man . There was no info anywhere I could find !!
To note...I got the used instrument cluster and put in the tach....works great.....in the old tach the resistance was not correct for the coil wrapping as described in the post that was referred to me ...no broken connections so I’m at a loss...still wanna figure it out! Lol
Basically three conditions for failure of coils. 1. Open circuit 2. Complete short 3. Insulation breakdown between several windings resulting in localised short and change in spec resistance. Resistance is reduced. Recently repaired an 83 Honda cbx for someone which has a dc excited ac generator. Dc excitation provided by the battery which is regulated by rectification of generator ac voltage. It controls the regulated voltage by varying the magnetic field up and down. Rotor should measure between 4 to 7 ohms which excites outer coil generating the required magnetic field. Basically on inspection the regulator had failed which seemed a simple fix however measuring the rotor showed 1 ohm. So basically at 12 volts the load current was approx 12 amps which fried the regulator. Initially the guy had replaced the regulator and fried the new one also. In the end both regulator and rotor needed replaced and all fine now. New rotor measured 5.6ohms.
